1. Field of the Invention
This invention relates to a semiconductor light emitting device and a method for manufacturing the same, more particular to a semiconductor light emitting device with a lateral structure.
2. Description of the Related Art
Referring to FIG. 1, a conventional process for manufacturing a semiconductor light emitting chip 1 with a lateral structure comprises: (a) epitaxially growing an epitaxial layer unit 12 on an epitaxial substrate 11, the epitaxial layer unit 12 being made from a GaN series semiconductor material and including a n-type cladding layer 121 that is in contact with the epitaxial substrate 11, a p-type cladding layer 122, and an active layer 123 disposed between the n-type and p-type cladding layers 121, 122; (b) etching the epitaxial layer unit 12 so as to expose partially the n-type cladding layer 121 and to define a plurality of epitaxial regions 15; (c) forming a first electrode 13 disposed on and in ohmic contact with the exposed n-type cladding layer 121 in each of the epitaxial regions 15, and a second electrode 14 disposed on and in ohmic contact with the p-type cladding layer 122 in each of the epitaxial regions 15; and (d) cutting the epitaxial layer unit 12 and the epitaxial substrate 11 to obtain a plurality of semiconductor light emitting chips 1. The structure of the semiconductor light emitting chip 1 is shown in FIG. 2.
The epitaxial substrate 11 is made from a material on which the GaN series semiconductor material of the epitaxial layer unit 12 is easily grown. An example of the material of the epitaxial substrate 11 is sapphire.
In addition, a transparent conductive layer (not shown), e.g., an indium tin oxide (ITO) layer, may be formed between the second electrode 14 and the p-type cladding layer 122 to improve electric conduction of the chip 1.
When an external voltage is applied to the semiconductor light emitting chip 1, an electric current is generated and flows from the second electrode 14 toward the epitaxial layer unit 12 where the charge carriers, i.e., electrons and holes, are allowed to flow and spread laterally. According to the electroluminescence effect, the electrons are able to recombine with the holes within the active layer 123 of the epitaxial layer unit 12 and emit energy in the form of photons. Therefore, the semiconductor chip 1 is able to emit light from the epitaxial layer unit 12.
The aforesaid manufacturing process of the semiconductor light emitting chip 1 with a lateral structure is relatively simple. However, the epitaxial substrate 11 of the chip 1 has a low thermal conductivity that results in thermal accumulation during operation, thereby reducing the service life of the chip 1.
FIGS. 3 and 4 show a semiconductor light emitting chip 2 with a vertical structure and the manufacturing process thereof. As shown in FIG. 4, after epitaxially growing an epitaxial layer unit 22, which has a n-type cladding layer 221, a p-type cladding layer 222, and an active layer 223, on an epitaxial substrate 21, a permanent substrate 23 is bonded to the epitaxial layer unit 22 oppositely of the epitaxial substrate 21, and the epitaxial substrate 21 is removed. The permanent substrate 23 has a high thermal conductivity and is able to serve as an electrode. Another electrode 24 is subsequently formed on and in ohmic contact with the epitaxial layer 22 oppositely of the permanent substrate 23 at an elevated temperature. A semiconductor light emitting chip 2 with a vertical structure (as shown in FIG. 3) is obtained by cutting the epitaxial layer unit 22 and the permanent substrate 23.
The drawback, i.e., the thermal accumulation, associated with the chip 1 with the lateral structure can be overcome by the chip 2 with the vertical structure by virtue of replacement of the epitaxial substrate 21 having poor thermal dissipation with the permanent substrate 23 with a high thermal conductivity.
However, formation of the electrode 24 on the epitaxial layer 22 under an elevated temperature is conducted after adhesion of the permanent substrate 23 to the epitaxial layer unit 22. The high temperature process may cause deformation or deterioration of the permanent substrate 23 and an adhesive between the epitaxial layer 22 and the permanent substrate 23. Therefore, problems such as warping and electric leakage of the semiconductor light emitting chip 2 may occur.
Moreover, in the chips 1 and 2, the electrodes 14, 24 disposed above the epitaxial layer units 12, 22 may shade the light illuminated from the active layers 123, 223 of the epitaxial layer units 12, 22 and reduce the luminance efficiency of the chips 1 and 2. In addition, in the conventional methods, the chips 1 and 2 are generally packaged individually. A subsequent series or parallel connection of the chips 1 or 2 results in a relatively large size of a light emitting product made from the chips 1, 2 and a complicated design for the circuit.